In a broadcast to the nation, Volodymyr Zelenskyy said: "We are defending our country, we fight for our country and we protect our country."

Ukraine would not be giving up its independence, he added.

"Independence and the right to live in our own country is the highest value," he said in the televised address.

Ukraine 'attacked from Russia, Belarus and Crimea' - latest live updates

Mr Zelenskyy said Russia attacked Ukraine "early in the morning just like fascist Germany did during the Second World War".

Russia and Ukraine are now on different sides of history and Russia is "on the side of evil", the president said.

Russian nationals, however, will decide for themselves what side they want to be on, he added.

Russian citizens who have a "conscience" should "stand against the war", he continued, saying Russia had an "evil desire to destroy the Ukrainian nation".

He asked anyone who has military experience to make themselves available.

Ukraine has wounded soldiers, he said, and appealed for blood donations to help treat them.

Weapons will be issued to any Ukrainian who wants one.

The enemy has suffered "serious losses", Mr Zelenskyy said.

Ukraine has cut diplomatic ties with Russia, and Mr Zelenskyy has introduced martial law in all territories.

Advising people to stay at home, he said "we are strong, we are ready for everything".

Ukraine's banking system has enough resources to protect the country's interests, he said.

Russian President Vladimir Putin said he had ordered a "specialised military operation", heralding the beginning of the invasion.

Sky News correspondents heard explosions in Kyiv and Kharkiv. We understand that borders have been breached in at least four areas of Ukraine.